The improvement of strength of ceramics has been indispensable for the increase of strain-to-fracture of them. Typical prior arts developed from such a viewpoint include the following.
The strength of silicon nitride ceramics has been accomplished by preventing defect structure causing in the ceramics in the process of production, and reducing the size of particles of them. For example, as shown in "J. Ceram. Soc. Jpn., 103 4!, pp. 407-408 (1995)", a material with high strength developed by using a sintering aid for controlling grain growth and performing sintering carefully at a temperature causing no grain growth has been reported. In addition, as shown in "J. Ceram. Soc. Jpn., 97, pp. 872-874 (1989)", a silicon nitride with high strength has been obtained by using a component to be dissolved to form a solid state in silicon nitride particles during sintering as a sintering aid, and controlling sintering thereby.
However, the above methods involve the following problems, and the solution thereof has been demanded fairly.
In order to prevent defect structure causing in the ceramics in a process of production, and reduce the size of particles of them, extremely minute process control is required as shown in the above examples. For example, as shown in "Locus and Results of advanced Research and Development of Fine Ceramics, edited by Fine Ceramics Research Association, 1993", it is required with a view to improving strength of the ceramics to repeat a vast amount of experiments and analysis, for making a thorough investigation of many factors and solving them successively. Because of these situations, the increase of strain-to-fracture owing to the improvement of strength of the ceramics has caused problems of an increase in cost and a lack in reproductivity, which have restrained the materials from being used for industrial utilization.